Evolutionary theorist Charles Darwin thought the voyage of the Beagle was a "magnificent scheme" allowing him to spend time "larking round the world".

His delight at the five-year cruise is chronicled in a letter, available online for the first time.

The note is one of nearly 5,000 from and to the scientist held in a database at the University of Cambridge.

The Darwin Correspondence project includes summaries of a further 9,000 letters, written from the age of 12.

In some of his earliest letters, he recounts talking to his sister Caroline, who had asked him about his personal hygiene.

"I only wash my fe[e]t once a month at school, which I confess is nasty, but I cannot help it, for we have nothing to do it with," he wrote.

Dr Alison Pearn, co-director of the Darwin Correspondence project, says it is insight like this that makes the letters so special.

"I think the human side is what is arresting about the letters," she said. "There is such an interesting and exciting mixture of very cutting-edge science and very personal revelations about his life and family."

Different paths

Darwin was a prolific letter writer, exchanging correspondence with nearly 2,000 people during his lifetime (1809-1882). Nearly 14,500 of his letters are known to exist, with the biggest collection residing in Cambridge.

His theory on evolution has influenced many science disciplines

"Letters were absolutely essential to what Darwin was doing," said Dr Pearn. "This is how he gathered data, how he gathered ideas, how he discussed ideas."

As well as other scientists, Darwin courted diplomats, clergymen, gardeners and pigeon fanciers.

"Pigeons are one of the organisms that Darwin investigated in great detail, in particular to study variation under domestication," said Dr Pearn.

"Breeding was so wide spread at the time that it was easy for him to tap into a network of people."

The letters also detail his dealings with other intellectual heavyweights of the time.

These included well known naturalists such as Alfred Russel Wallace, who collected specimens in the Amazon and Malay Archipelago and independently formulated a theory of evolution by natural selection.

In a letter from May 1857, contained in the new archive, Darwin replied to Wallace who had reported some of his own conclusions in the Annals and Magazine of Natural History and in a letter sent to Darwin on 10 October 1856.

"I can plainly see that we have thought much alike and to a certain extent have come to similar conclusions," wrote Darwin.

Darwin was one of the most important figures in the history of science. He changed forever our understanding of life on Earth.

John van WyheDarwin Online

"I agree to the truth of almost every word of your paper; and I daresay that you will agree with me that it is very rare to find oneself agreeing pretty closely with any theoretical paper; for it is lamentable how each man draws his own different conclusions from the very same fact."

Darwin and Wallace eventually published their theories in a joint paper in 1858, a year before Darwin published On the Origin of Species.

Letters from throughout this period map out the evolution of his ideas and publications.

Complete collection

The Darwin Correspondence project has existed offline since 1974. It has so far published 15 volumes of the scientist's letters as books.

The Beagle set off for South America in 1831

An agreement with the publisher of the books means the new website will offer digitised versions of the texts freely available to anyone four years behind the hard copies.

Nearly 5,000 pieces of correspondence will be fully searchable when the site launches on Thursday 17 May.

"This is good news for everyone," said Dr John van Wyhe, project director of Darwin Online, a separate project also based at the University of Cambridge.

"Darwin was one of the most important figures in the history of science. He changed forever our understanding of life on Earth."

Set up in 2002, Darwin Online is putting Darwin's publications and non-correspondence manuscripts on the web. It also has downloadable audio files and images.

The most recent addition, the diaries of Darwin's wife, Emma Darwin, cover six decades of the couple's life together.

"My aim was to have a website that has everything else," said Dr van Wyhe. "We complement each other."